This invention generally relates to the manufacture of golf balls, and more particularly, to a mold-half for molding various layers on golf balls.
Modern day golf balls can be generally classified as one-piece, solid and wound. Solid balls can be one-piece or two or more piece constructions. One-piece solid balls are injection or compression molded from a homogeneous mass of material with a dimple pattern molded thereon. These are inexpensive and very durable, but do not provide great distance because of their lower compression. They tend to have a soft feel when struck with the club face.
Two piece solid balls are made by molding a cover about a solid core. These are one of the most popular types of balls in use today. These balls can have a hard xe2x80x9ccutproofxe2x80x9d cover which goes a greater distance, and generally have lower spin rates. Three-piece solid balls may be made by molding a cover around a solid core comprising a solid center with a mantle layer molded about the outside of the center.
Wound balls are made by molding a cover about a wound core. A center is typically made of rubber and can be solid or have a fluid-filled center. The wound core is prepared by winding a lengthy thin thread of elastic material about the center. The wound core is then covered with a durable cover material. Wound balls are generally softer and provide more spin, resulting in increased control over the ball. As a result of their more complex construction, the wound balls generally require a longer time to manufacture and are more expensive to produce than solid balls.
The covers on these golf balls are made from materials, such as synthetic balata ionomer resins, or urethane polymers. A prior art mold-half for use with these materials is shown in FIGS. 1-3. The mold-half 10 comprises a cavity 15, a land area 20 surrounding the cavity 15, a circumferential groove 30 within the land area 20, and a plurality of vents 35 in fluid communication with the circumferential groove 30. The vents 35 and groove 30 are spaced from the cavity. The surface 40 of the cavity 15 is textured with dimple forming projections 45, which produce a dimple pattern on the cover of the golf ball. Additionally, the land area 20 includes an upper surface 50 and a radially outer surface 55. The portion of the land area between the cavity 15 and the groove 30 is designated 20a. The portion of the land area radially outward of the groove is designated 20b. Each vent 35 includes a vent side wall 60. The mold-half 10 further includes a projection 65 extending radially outward from the land area 20.
A pair of mold-halves 10 are clamped together under pressure to form a spherical cavity therein. As the mold-halves 10 are clamped the cavities contain a core or center and material to form hemispherical portions of the cover. The mold-halves 10 are held together until the cover material is cooled and then opened to demold the ball. As this mold is closed, excess cover material between the land areas 20a is squeezed into the groove 30 and flows into vents 35, which convey the material to the exterior of the mold. Notably, the groove 30 is configured to form an alignment ring for a separate process in the manufacture of the golf ball and is not specifically designed to cooperate with the other features of the mold to facilitate compression molding of material. The cavity 15 still contains excess cover material but there is no passageway from the cavity to convey this material. The process is farther complicated by the inability to convey the excess material within the cavity out of the cavity. The increased internal pressure due to the thermal expansion of the molded ball assembly causes this excess material to separate the mold and allows jagged flash to form around the molded cover of the ball.
Consequently, a need exists for an improved mold-half for manufacturing a golf ball cover. The mold-half should minimize the likelihood of mold separation, reduce the number of cracked or defected covers produced, and lower the potential for jagged flash formation around the molded cover or other molded layer of the golf ball.
The present invention is an improved mold-half that is particularly useful in casting golf ball covers. In particular, the mold-half is useful for molding a thin veneer cover over a golf ball subassembly that includes a plurality of inner layers. The mold-half includes a hemispherical cavity and a land area surrounding the cavity. The land area has an upper surface and at least one vent defined in the upper surface spaced from the cavity. The land area also has a circumferential ledge adjacent the cavity and each vent.
Two mold-halves of the present invention are combined to form a mold. Joining the land areas of a pair of mold-halves creates a spherical cavity for receiving the subassembly. Additionally, a chamber is formed adjacent the cavity by the opposing ledges of the two mold halves, and opposing vent pairs each form a bore for releasing excess material from the chamber. The ledges and vents are operatively configured such that the flow of material is allowed primarily through the bores. Furthermore, the chamber is configured such that the volume of the chamber is sufficient to contain the material during flow from the cavity without allowing the mold-halves to separate.
Generally, the length of the circumferential ledge is between about 0.005 inches and about 0.05 inches and preferably the length of the circumferential ledge is about 0.015 inches. Additionally, the circumferential ledge is recessed from the upper surface of the land area by about 0.001 to about 0.01 inches, more preferably by about 0.005 inches. Further, each vent is spaced from the cavity wall by about 0.01 inches to about 0.02 inches. The preferred length from the cavity wall to each vent is about 0.015 inches. Further still, the depth of each vent is between about 0.025 inches and about 0.08 inches, and the preferred depth of each vent is about 0.03 inches. Typically, each vent has a length of at least between about 0.04 inches and about 0.08 inches with a preferred length of about 0.5 inches.
In one embodiment, the mold-half further includes a projection that extends radially outward along the entire circumference of the land area. The projection is located below the upper surface of the land area. The outer diameter of the projection is about 2.43 inches and the thickness of the projection is about 0.25 inches. An upper surface of the projection is situated about 0.38 inches below the upper surface of the land area.
According to the features of one embodiment, the land area includes a uniformly sloped surface extending between the upper surface of the land area and the upper surface of the projection. In addition, in one embodiment the cavity includes a plurality of projections for forming a plurality of depressions or dimples in the cover. In yet another embodiment, the land area contains a plurality of vents which preferably are spaced uniformly around the circumference of the land area.
The present invention is also directed to a mold for forming a layer of material around a golf ball subassembly. The mold includes a pair of mold-halves, where each mold-half includes a hemispherical cavity, a land area, and a circumferential ledge. The land area surrounds the cavity and includes an upper surface. The circumferential ledge is adjacent the cavity. The upper surface of one land area is configured to mate with the opposing land area and locate a portion of the material within the cavity.
The mold may also include vents extending from the ledge.